Rotating a multipart object

Question

I\'ve created an object that has about 7+ parts to it including its body and smaller parts that \'attach\' to it in different places. My goal is to rotate the entire object.

Answer 1

1. you are missing glMatrixMode calls

   If you are using only GL_MODELVIEW than it works (if lastly set active) but when your code grows longer and you add other calls you might broke this and suddenly your code will not work as expected (and very hard to debug). Therefore it is better to add glMatrixMode(GL_MODELVIEW); before any transformation chunk of code.

2. You are push/pop ing wrongly

   Your objects are nested so the matrices must be nested too. That means any part attached to owner part must start with the owners part matrix. So you need to have some hierarchy of the parts (assembly order) so you know what parts are attached to which ones and where.

   so You should have a list of parts connected to any part ... Something like:

   List part[noOfObj];
   

   so any part[i], i=<0,noOfObj-1> has children parts part[i][0,1,2...,part[i].num-1] connected to it (where num is size of the list). And part[0] is the main part. That changes things a bit but simple recursion helps:

   void part_draw(int ix) // this is just recursion call used by the main function do not use it directly
    {
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glTranslatef(subPosX[ix], subPosY[ix], subPosZ[ix]);
   
    glPushMatrix();            // this should not be here 
    glScalef(9.0, 1.75, 1.75); // this should not be here
    ..... // draw the object ix here
    glMatrixMode(GL_MODELVIEW);// this should not be here
    glPopMatrix();             // this should not be here
   
    for (int iy=0;iy

   Now beware that subPosX/Y/Z positions must be in parent part coordinate system. Also This will not work for cyclicly nested objects (loops) as that would lead to infinite loop causing stack overflow.